As used herein, the term "cremator" is intended to include incinerators and other furnaces for burning objects and materials other than coffins, e.g. any form of waste, or even other materials or objects, and the term should therefore be construed accordingly.
There are various known designs of cremators of the type having a primary combustion chamber for receiving through a charge door thereof a coffin or other object for cremating by means of a burner directed into the primary combustion chamber, and a secondary combustion chamber, separate from the primary combustion chamber, through which are passed the gases, particulates and other exhaust materials from the primary combustion chamber to ensure maximum burning of combustible material during the cremation process. One example of such a dual combustion chamber furnace is disclosed in our published UK patent application GB-A-2180630.
Such dual combustion chamber furnaces are advantageous over known single combustion chamber furnaces, because of the higher degree of burn-off of combustible material from the coffin or other object being cremated. In fact, nowadays such dual combustion chamber cremators are generally essential in order to satisfy legal, environmental and aesthetic requirements as regards waste emissions from cremator installations.
Over recent years in many countries of the world legislation has been introduced which places even more stringent requirements on the content of waste gases emitted from cremator installations, particularly with respect to ensuring complete combustion of gases and fine particulates entrained therein exiting from the combustion chamber(s) before being released from the cremator via an exhaust flue. Laws now generally required that the waste gases exhausted from the combustion chamber(s) are retained in a retention zone heated to a temperature of at least 850.degree. C. (as is the case in Europe) for a period of at least two seconds, before being allowed to pass to the exhaust flue and released into the atmosphere. This period of retention of the waste gases in the heated retention zone ensures complete combustion of gases and any remnant or fine particles entrained therein which may not have been fully burned during the main combustion process.
There have been various known attempts at designing cremator furnaces which include such a heated retention zone in addition to the preferred primary and secondary main combustion chambers. Once such known design of cremator is shown in FIGS. 1A and 1B of the accompanying drawings. Here the cremator comprises a main, primary combustion chamber C1 into which may be loaded via charging door D1 a coffin or other object to be cremated. The primary combustion chamber C1 has a first burner/air inlet jet B1 by means of which the coffin undergoes primary combustion. Located beneath the primary combustion chamber C1 is a secondary combustion chamber C2 which is provided with a second burner/air inlet jet B2 to accomplish secondary combustion of waste gases and gas-born material exhausted from the primary combustion chamber C1. In this particular example the cremator has an additional, tertiary, combustion chamber C3, again with its own, third, burner/air inlet jet B3 which is located beneath the secondary combustion chamber C2. All three combustion chambers C1, C2 and C3 are typically heated by their respective burners to up to around 1300.degree. C. The arrows in FIGS. 1A and 1B illustrate schematically the general path of waste gases within the cremator.
Having passed from the primary combustion chamber C1 through the secondary and tertiary combustion chambers C2 and C3, the waste gases pass up and through ducts around the primary combustion chamber C1 into a retention chamber R which is located above the primary combustion chamber C1. The gases remain in this retention chamber R for a short period of time before passing up and out thereof via exhaust flue F. The temperature of the retention chamber R is maintained at the required level (e.g. at least 850.degree. C.) either by the temperature of the waste gases themselves or, if necessary, by use of an additional burner (not shown) provided in the retention chamber itself. It can generally be considered that in this known construction of cremator, it is the secondary and tertiary combustion chambers C2, C3 as well as the retention chamber R itself which together constitute the heated retention zone which by law is required to be present.
This known construction of cremator has several disadvantages: one is that each chamber or region through which waste gases pass is discrete and provided with its own respective burner. This leads to uneconomical use of fuel and power and also demands a more complex operating control system for the whole apparatus. The cremator of this design is also bulky and necessarily of more complex and costly construction.
In another known cremator design which employs a retention chamber to temporarily accommodate waste gases having been exhausted from the main combustion chamber(s), the retention chamber is located not above the main combustion chamber, but alongside it. This construction of cremator leads to similar disadvantages as regards economy of operation, bulkiness, complexity, cost, as the first known design of cremator discussed above.